In RA, NOTCH3 signaling from the endothelium acts primarily on mural cells, which in turn stimulate sublining fibroblasts along a spatial axis21 as seen in the decreasing NOTCH3 gene expression from SA−3, SA−0, SA−2, to SA−1 in the multiome cells (Supplementary Fig. 4b). Here, STAG1 is linked to rheumatoid arthritis.